Graphene oxide does not seem to improve the fracture properties of injection molded

ABSTRACT: Scientific literature presents a number of examples in which the mechanical properties of materials are significantly improved by adding small amounts of nano-particles. In many cases, the addition of such nano-particles is performed on polymer-matrix composites, with reported improvements in mechanical, optical, thermal or electrical properties. Therefore, the potential of this technology is huge and a great deal of research work is being performed with the aim of generating new advanced engineering materials. However, this paper presents the other side of the coin. The authors have introduced small amounts of Graphene Oxide (up to 1%) in PA6 with the aim of studying their effect on the fracture properties of the resulting composites. For the particular conditions analyzed here, no improvements in the fracture behavior (in both cracked and notched conditions) have been observed (a similar conclusion may be obtained for the tensile behavior). Other types of material properties were not covered in the analysis. Sharing this kind of (negative) results may save other researchers time and budget, and it is a much more common practice in other fields of science.The authors of this work would like to express their gratitude to the Spanish Ministry of Science and Innovation for the financial support of the project PGC2018-095400-B-I00 “Comportamiento en fractura de materiales compuestos nano-reforzados con defectos tipo entalla”, on the results of which this paper is based

Mechanical, dynamic, and thermomechanical properties of coir/pineapple leaf fiber reinforced polylactic acid hybrid biocomposites

Natural fiber‐based polymer composites have been widely studied to substitute synthetic materials. In this research, pineapple leaf fibers (PALF) and coir fibers (CF) were loaded into a polylactic acid (PLA) matrix to develop composite materials with improved mechanical and thermal properties, which could be potentially applied as biodegradable food packaging. Biocomposites with different fiber ratios were manufactured using an internal mixer plasticizer and a hot press machine. Mechanical and thermal analyses of the obtained composites were carried out and the results were compared with those of pure PLA. Scanning electron microscopy (SEM) was used to observe the microstructural failure of the composites. Mechanical tests indicated that all the composites had higher tensile and flexural modulus, compared to those of neat PLA. Also, strength values were increased upon addition of PALF, while impact tests showed enhanced strength results upon addition of CF. SEM findings confirmed the outcomes of the mechanical tests. DMA results confirmed that the storage and loss moduli of the CF/PALF/PLA hybrid composites increased with respect to those of the neat PLA, whereas the tan δ decreased. The coefficient of thermal expansion (CTE) of the PLA composites decreased with the addition of fiber reinforcements. Based on the results achieved in this investigation, the hybrid composite containing CF and PALF in a 1:1 ratio (C1P1) presented the optimum set of mechanical properties and improved thermal stability, which make it suitable for applications such as food packaging and structure components to help reduce the environmental loads

Bioinspired multilayered cellular composites with enhanced energy absorption and shape recovery

International audienceInspired by the multiscale configuration of the microstructure of cork, the paper describes the design, 3D printing, and evaluation of a new type of multilayered cellular composite (MCC) structure composed of hard brittle and soft flexible phases. The mechanical behavior of 3D printed MCC structures have been investigated both experimentally and numerically. The experiments show that the MCC structure absorbs four times the amount of energy of a conventional cellular configuration under compressive strains up to 70%. Finite element simulations and 2D digital image correlation (DIC) also show that the multilayered architecture provides a more uniform strain distribution and higher stress transfer efficiency, with a resulting progressive failure mode rather than a catastrophic one. Cyclic loading tests demonstrate that the MCC structure also possesses exceptional shape recoverability under compressive deformations up to 40%. These remarkable performance characteristics result from synergies between the properties of the two constituent materials and the chosen multilayered cellular microstructure. The soft phase, in particular, plays a pivotal role in absorbing elastic energy during loading and then releasing the stored energy while unloading. The volume fraction of the soft phase is also essential to control energy absorption and the transition of failure modes. The deformation mechanisms demonstrated here are robust and applicable to other architected cellular materials across multiple length scales and suggest new ways to design lightweight and high-resilience structural materials.Inspiré par la configuration multi-échelle de la microstructure du liège, cet article décrit la conception, l'impression 3D et l'évaluation d'un nouveau type de structure composite cellulaire multicouche (MCC) composée de phases dures et fragiles et de phases souples et flexibles. Le comportement mécanique des structures MCC imprimées en 3D a été étudié à la fois expérimentalement et numériquement. Les expériences montrent que la structure MCC absorbe quatre fois la quantité d'énergie d'une configuration cellulaire conventionnelle sous des contraintes de compression allant jusqu'à 70%. Les simulations par éléments finis et la corrélation d'images numériques (DIC) en 2D montrent également que l'architecture multicouche permet une distribution plus uniforme des déformations et une meilleure efficacité du transfert des contraintes, avec pour résultat un mode de défaillance progressif plutôt que catastrophique. Les essais de chargement cyclique démontrent que la structure MCC possède également une capacité exceptionnelle de récupération de la forme sous des déformations en compression allant jusqu'à 40 %. Ces remarquables caractéristiques de performance résultent des synergies entre les propriétés des deux matériaux constitutifs et de la microstructure cellulaire multicouche choisie. La phase molle, en particulier, joue un rôle central dans l'absorption de l'énergie élastique pendant le chargement et la libération de l'énergie stockée pendant le déchargement. La fraction volumique de la phase molle est également essentielle pour contrôler l'absorption d'énergie et la transition des modes de défaillance. Les mécanismes de déformation démontrés ici sont robustes et applicables à d'autres matériaux cellulaires architecturés sur plusieurs échelles de longueur et suggèrent de nouvelles façons de concevoir des matériaux structurels légers et à haute résilience

Synthetic polymer-based membrane for lithium Ion batteries

Efficient energy storage systems are increasingly needed due to advances in portable electronics and transport vehicles, lithium-ion batteries standing out among the most suitable energy storage systems for a large variety of applications. In lithium-ion batteries, the porous separator membrane plays a relevant role as it is placed between the electrodes and serves as a charge transfer medium and affects the cycle behavior. Typically, porous separators membranes are comprised of a synthetic polymeric matrix embedded in the electrolyte solution. The present chapter focus on recent advances in synthetic polymers for porous separation membranes, as well as on the techniques for membrane preparation and physicochemical characterization. The main challenges to improve synthetic polymer performance for battery separator membrane applications are also discussed.Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019, UID/QUI/50006/2019, UID/QUI/0686/2016 and UID/EMS/00151/2019. The authors thank FEDER funds through the COMPETE 2020 Programme and National Funds through FCT under the project PTDC/FIS-MAC/28157/2017, Grants 38 SFRH/BPD/117838/2016 (JNP). and SFRH/BPD/112547/2015 (C.M.C). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-3-R (AEI/FEDER, UE) (including the FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06